A heat shrinkable plastic product uses a property of being shrunk by heating and is widely used as a film for a shrinkage package, a shrinkage label, or the like. Among them, polyvinyl chloride (PVC), polystyrene, and polyester based plastic films, and the like, have been used as a label or cap seal of various containers, or the like, or used as a direct package material, or the like.
However, a film made, of polyvinyl chloride is a regulation object since at the time of burning up the film, materials generating hydrogen chloride gas and dioxin may be generated. In addition, when this product is used as a shrinkage label of a polyethylene terephthalate (PET) container, or the like, at the reusing the container, a troublesome process of separating the label and the container should be performed.
Further, in the polystyrene based film, stability in work depending on a shrinkage process may be excellent and an appearance of the product may be good, but chemical resistance may not be excellent, such that there is a problem in that at the time of printing, an ink having a specific composition should be used. Further, the polystyrene based film has a disadvantage in that since storage stability at room temperature is insufficient, the film may be spontaneously shrunk, such that a dimension thereof may be changed.
In order to solve the above-mentioned problems, a film made of a polyester resin has been studied and developed as a film capable of replacing the films made of the above-mentioned two raw materials. Meanwhile, as a use amount of the PET container is increased, a use amount of a polyester film capable of being easily reused without separately separating a label at the time of reuse has been gradually increased, but a heat shrinkable polyester film according to the related art had a problem in view of shrinkage characteristics. That is, there was a problem in that wrinkles at the time of shrinkage or non-uniform shrinkage during molding was frequently generated due to a rapid change in shrinkage behavior. In addition, since a shrinkage property of the polyester film at a low temperature is decreased as compared to the polyvinyl chloride based film or the polystyrene based film, in order to complement this disadvantage, the polyester film should be shrunk at a high temperature. In this case, there was a problem in that PET container may be deformed, or a white-turbidity phenomenon may be generated.
Therefore, research into a polyester based copolymer of which a shrinkage rate is excellent and a shrinkage property at a low temperature is improved has been required.